Protective electronic tube and circuit



, 1956 G. WILKES ROTECTIVE ELECTRONIC TUBE AND CIRCUIT Aug. 21

Filed Aug. 24, 1950 PROTECTIVE ELECTRONIC TUBE AND CIRCUIT Gilbert Wilkes, Chevy Chase, Md., assignor to the United States of America as represented by the Secretary of the Navy The present invention relates to a protective electronic tube and its circuit and more particularly to a multipleelectrode tube which is useful in controlling the flow of ultra high frequency energy through a Waveguide.

Such devices have been found useful in ultra high frequency pulse radiating and receiving systems wherein many such systems employ a single device which serves both as a transmitting and receiving antenna. The device of the present invention makes it possible for high energy transmitter pulses to be introduced in a waveguide, also used by the receiver, in such a manner that the receiver is not paralyzed or permanently damaged by the high energy of the transmitted pulse. Also pulse radiating systems may be operated in close proximity to one another without injury to their receiving equipment.

In common parlance, a protective, gas-discharge device has come to be known as a T-R box, which is an abbreviation for the term transmission-reception box.

The prior art T-R boxes have generally assumed the form of a gas-enclosing metallic resonant casing having a glass or ceramic window through which the radio frequency energy passes. The casing is also provided with discharge electrodes to effect ionization of the gas Within the enclosure in response to high intensity received energy.

The ionization of the gas effectively destroys the resonant condition of the casing to thereby completely block the passage of energy through the casing. Thus, when the transmitter pulses, the emitted energy passes along the waveguide and out the antenna, but it is prevented from entering the receiver by the T-R box. However, the de vice permits a received impulse to enter the receiver unattenuated.

These previous devices, however, presented a number of disadvantages, such as the difliculty in obtaining adequate seals between the ceramic window and the metal casing, as well as the accurate positioning of the window at a point of voltage maximum so as not to destroy the electrical characteristics of the device. Another disadvantage was that the passage of energy through the waveguide was either unattenuated or else blocked completely, which left much to be desired as far as regulation was concerned.

The present device offers many improvements over those in the prior art, such as case of installation wherein the tube is inserted through a hole in the waveguide, eliminating the need for a resonant T-R box. Furthermore, the present tube permits regulation of the energy over a range of amounts and does not completely block the waveguide or leave it completely unobstructed. Also there is a small amount of ionization in the tube at all times which results in instant operation of the device should the received energy become too large.

An object of the invention is the provision of a tube which prevents injury to the crystal detector in a radar apparatus.

Another object is the provision of a tube and circuit ice which is inserted through the waveguide and does not require a T-R box.

A final object is the provision of a protective tube for' a crystal detector wherein the tube has a pair of closely spaced electrodes between which a continuous discharge may be maintained and also a relatively remotely spaced electrode for causing a second discharge throughout the tube.

Other objects and features of the invention will become apparent to those skilled in the art as the disclosure is made in the following detailed description of a preferred embodiment of the invention as illustrated in the accompanying sheet of drawing in which Fig. l is a perspective view of the tube showing its internal structure.

Fig. 2 is a schematic diagram of the circuit used in the invention.

Referring now to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in Fig. l a space discharge tube, indicated generally as 10, comprising an envelope 11 preferably made of hard glass, such as Pyrex and the like.

Enclosed within the envelope 11 is an attenuated atmosphere preferably of one or a mixture of the group of monatomic inert gaseous elements, such as neon. Other gases could be used but probably greater stability and longer life of the tube will result when the residual atmosphere is completely inert in a chemical sense, hence the rare gases are preferred.

Mounted in one end portion of the tube are two electrodes 12 and 13 which are shown as one inside the other, and it can be clearly seen in Fig. 1 that the electrodes 12 and 13 are essentially conical in shape and earth metal oxide or a mixture of such oxides may be applied to assist in the emission of electrons from these electrodes. j

Provided at a location situated relatively remote from the electrodes 12 and 13, is an additional electrode 15 which is placed at one extremity of a clear, unobstructed portion 16 of the envelope 11. Leads 17, 18 and 19 are used to supply power to electrodes 12, 13 and 15 respectively, and the operation of tube 10 will be more fully described hereinafter.

In the schematic diagram of Fig. 2, it is to be noted that the tube 10 is shown conventionally, for simplicity, rather than as a true elevation view. The waveguide 21 is any well known type-of device which is used to transmit ultra high frequency energy, and has inserted through it so as to be transversely across the path of the radar waves, the portion 16 of tube 10. Adjacent to, and closely surrounding, tube 10 where it passes through waveguide 21 are chokes 30 which are provided to prevent loss of energy around the tube.

Also connected to Waveguide 21, but at a little distance beyond the point where tube 10 passes through the waveguide, is a conventional crystal detector 22, such as a germanium or selenium crystal as is generally used in high frequency receiver circuits and it is this crystal which the tube 10 acts to protect from damage. It, is to be noted that waveguide 21 continues on a little past:

' the crystal and terminates in closed end 23, and that the Patented Aug. 21, 19 56.-

This close approach de-.

3 crystal is so spaced from the closed end 23 that it is positioned at a, point of current. node.

Connected across the output of detector 22 is an amplifier 24 which receives the detector output by means of Ieads-Z-Sand 26., the latter of which is grounded as shown. The ungroundedoutput lead 27 of the amplifier 24: is con-- nected tci,lead;19 of electrode 15=within 'tube.10, while between; lead 27 and ground there is connected a condenser 28 and resistor 29 in parallel. This condenser.- resistor combination has a delaying action. on. the responseof tube 10, as will be more fully described hereinafter.

A suitable voltage of approximately. 75 vjolts, as here shown by battery 31, is applied. to leads 17.and:181 to thereby maintain a continuous discharge between electrodes. 12and.13, so, that tube-is kept partially ionized for instant response.

In operation, the tubev 1.0 of Fig. 1. has. a relatively low voltage, usually well below 100 volts D. 0., applied to electrodes 12 and 13, whereby adischarge takes place between them asshown by a resulting glow. This maintains a source of ionization in the tube, so that when a voltage is applied between lead 19 and either of the other leads, a discharge takes place at once between electrode 15 and one of the other electrodes. By proper choice of the nature and pressure of the residual gas in the tube 10, this discharge may providepowerful ionization of the column of gas in the portion 16 of the tube. Thisphenomenon is useful in the circuit of Fig. 2 as will now be described.

Intheoperation of Fig. 2, ultra high frequency energy, such as radar waves, enters the waveguide 21 from the left and passes through the portion 16 of tube 10 which is.

inserted transversely across the waveguide. When no dischargeis taking place through electrode 15, and therefore through portion 16, thetube constitutes no particular obstruction to the passage of the radar waves through it, and they, therefore,progress along the waveguide to the crystal detector 22 which they actuate.

The rectified impulses from crystal 22 pass along leads 25,.and 26 to enter amplifier 24 where they are amplified and utilized as desired. Some of the amplifier output is, however, returned through lead 27 and ground to tube 10,-where it is applied to electrodes 15 and 12. It can beclearly seen, from the circuit of Fig. 2, that the varying output of, crystal 22, after ithas been amplified by 24, is appliedas a varying plate voltage for electrode 15. It is this varying potential which acts to vary the discharge in.16, and therefore thedegree of blockage in the waveguide,'so as to protect the crystal from strong signals.

In contradistinction to the operation of most T-R tubes, wherein they. either completely block the waveguide or else ofier no obstruction to the passage of energy therethrough,,the.present protective tube resembles a valve in itsoperation and can control the passageof energy in any degree between the two extremes. This valve-like control exerted by the tube is accomplished in the followingmanner. It will be recalled that the keep-alive voltage across electrodes 12 and 13 maintains ionization in the lower portion of tube 10 at all times. Now whenthe varying potential from the output of amplifier 24 is applied to electrode 15, which is relatively remote from the other electrodes, it has been found that a portion of the, ionization from the lower part of the tube will move up into the narrow portion 16 depending upon the amount of'pote'ntial on electrode 15. Effectively the ionization is drawn up into the neck of the tube in proportion to the potential on 15, and since this potential is proportional to the, output of crystal 22, then the degree to whichthe passage of energy along the waveguide is restricted, will depend upon the signal on the crystal. The stronger the signal thetnore the ionization in portion 16 of the tube tocutofi more of the energy reaching the crystal. Should the potential on electrodelS be unduly large so as to cause a-powerfuldischar'ge in the tube, this discharge which provides a dense cloud of ionization consisting of a mixtureofi electrons. and positive ions, is substantially opaque to the radar waves. in waveguide 21, thereby automatically blocking the Waveguide and preventing excessive energy from striking the crystal.

Some energy should get past the tube 10, however, in the normal operation of the device, and this is accomplished by shunting the condenser 28 and the resistor 29 across conductors 26 and 27. While the condenser 28 is acquiring a charge, its voltage rise is delayed so that energy may flow, for a brief interval, through the waveguide 21 before the electrode 15 discharges and shuts off the flow. The resistor 29 enables the condenser to discharge between actuations'.

The values of capacitance and resistance of these elements are so selected that initially energy may flow past the tube 10 for a very brief interval, and before the intensity of flow has become very great, so that no injury to the detector occurs, but. as soon as danger of injury arises the circuit automatically shuts off any flow of'radar energy by means'of. the discharge from electrode 15.

From the above description of the invention and the manner in which it operates, it is obvious that the de vice presents a. novel protective tube and circuit which effectively protects the crystal detector in ultra high frequency equipment by providing a wide range of regulation. Also atube which is inserted through a waveguide and which does notrequire the use of a T-R box to effect its attenuation of waves passing through the waveguide.

It should beunderstood, of course, that the foregoing disclosure relates to only a preferred embodiment of the invention andthat it is intended to cover all changes and modifications of the example of the invention herein chosen for the purposes of the disclosure, which do not constitute departures from the spirit and scope of the invention as setforthin the appended claims.

What is claimedis:

1. A protective circuit. for a detector comprising a waveguide a protective dischargetube interposed in said waveguide, a crystaldetector also interposed therein beyond the tube with respectv to the source of the waves, means connected across the output of said detector for producing a relatively high voltage in response to actuation of,the-detector by, the waves, and means connected across-the output of the high voltage means and to the discharge; tube for feeding said voltage to the tube to cause a. dischargeto occur therein, whereby the further flow of waves is substantially prevented.

2 The circuit of. claim 1 including also electrical delay means connected across the output of said high voltage meanswhereby theenergization-of the discharge tube is retarded, said-delay means including a capacitor and a resistor.

3; Aprotective circuit. comprising a waveguide, an elongated gaseous discharge tube having relatively large and small portions, the small portion of said tube being interposed transversely through said waveguide, a crystal detector also interposed .in said waveguide beyond the tube from the source of the waves, means for producing a relatively high voltage in response to actuation of the detector by the waves, and means for feeding said voltage to the small portion of the tube to cause a discharge to occurtherein, whereby the discharge substantially prevents further flow of waves through the waveguide.

4. A protective circuit comprising a waveguide, an elongated gaseous discharge tube having relatively large andsmall portions, twoelectrodes in said large portion, a thirdelectrode in said small portion located relatively remotefrom the other electrodes, the small portion of said tubev being interposed transversely through said waveguide, a crystal detector interposed in saidwaveguide, meansfor maintaining a; discharge in the large portion of thetube between the first two electrodes, means for producing a relatively high voltage in response to actuation of the detector, and means for feedingsaid voltage to the third electrode, whereby a part of the discharge moves from the large to the small portion of the tube to substantially block the waveguide.

5. A circuit for protecting a detector from unduly large signals comprising a waveguide, a gaseous discharge tube having relatively large and small portions with the small portion interposed in the waveguide, a detector also interposed in the Waveguide, means for maintaining a discharge in the large portion of said tube, means for producing a voltage which varies as the output of said detector varies, and means for applying said voltage to an electrode disposed in the small portion of the tube, whereby a discharge occurs in said small portion of the tube proportional to the output of the detector, said discharge acting to attenuate wave flow through the waveguide.

6. A protective circuit for a detector comprising a waveguide, a gaseous discharge tube interposed in said waveguide, a detector also interposed in the waveguide,

circuit connected in parallel across the output of the amplifying means as a delay means to retard energization of the tube, whereby the degree of flow through the Waveguide is regulated in proportion to the output of the 10 detector.

References Cited in the file of this patent UNITED STATES PATENTS 15 2,034,572 Found Mar. 17, 1936 2,413,171 Clifford et al Dec. 24, 1946 2,454,761 Barrow et a1 Nov. 30, 1948 2,472,196 Cork June 7, 1949 2,505,534 Fiske Apr. 25, 1950 

